NS 190ct2002GENDER IDENtiTy
ltmaybe your brain not your genitals that decides what sex you
really are

OUR brains could be hard-wired to be male orfl-male long before
we begin to growtestes or ovaries in the womb. This discovery
might explain why some people feel trapped in a body that's the
wrong sex, and could also lead to tests that reveal the true "brain
sex" ur babies born with ambiguous genitalia. Till now, the
orthodoxy among developmental biologists has been that embryos
develop ovaries and become female unless a gene called SRYon the
Y chromosome is switched on. If this gene is active, it makes
testes develop instead. This switch is seen as the key event in
determining whether a baby is a girl or a boy. Onty after the
gonads form and flood the body with the appropriate hormones,
the theory goes, is the sex of our minds and bodies determined.
But in a study of mice, a team at the University of California,
Los Angeles, has now found that males and females show differences
in the expression of no fewer than 50 genes well before SRYswitches
on. "It's the flmt discovery cvf genes differentially expressed
in the brain," says Erlc Vilain, who led the UCLA team. "They
may have an impact on the hard- wired development of the brain
in terms of sexual differentiation independent of gonadal induction."
irilain is presenting details of seven of the 50 genes to the
annual meeting of the American Society af Human Genetics in Baltimore
this week. Three of these genes are dominant in females and four
are dominant in males. The next step for Vilain and his team will
be to show that the genes in question really do influence brain
sexuality - and notjust in mice. This is likely to be a much tougher
preposition than merely showing there are differences in expression.
But if the findings are confirmed, they could one day yield blood
tests that allow doctors to establish the brain sex of babies
born with genitalia that share features of both sexes. At present
doctors and parents have to guess which gender to assign fbr surgical
"correction". Robin Lovell Badge of the National institute
fbr Medical Research in London, who discovered the SRYgene, is
already looking at mice with a Y chromosome lacking the SRYgene,
to see if their brains and behaviour are in ariy way male despite
their lack of testes. "The growing feeling is that there
will be direct effects on the brain, anatomy and behaviour due
to X ory-linked genes," says Lovell Badge. "It's early
days yet, but we're pretty sure there are effects on some aspects
of aggression and reproductive behaviour independent crf gonadal
sex." Andy Coghlan *

Bunker busters set to go nuclear Fifty years after the first hydrogen bomb was detonated, nuclear
weapons are about to get a terrifying new role

DAVID HAMBLING

THE US government is set to fund research into a new type of
nuclear weapon that's designed to penetrate and obliterate deeply
buried targets such as underground weapons bunkers. Coming 5o
years after the world's first hydrogen bomb was detonated in the
Pacific, the news has alarmed scientists opposed to nuclear proliferation.
They say the thousands of tonnes of radioactive debris produced
by a bunker-busting nuclear weapon would not be contained within
the rock, concrete and soil above the target, but would contaminate
a wide area around it. Funding Of $15 million has been proposed
for research into the so-called Robust Nuclear Earth Penetrator
(RNEP), as part of the government's draft Defense Authorisation
Bill for 2003. But the bill has not yet been passed by the Senate
Committee on Armed Services, which as New Scien tis t went to
press was controlled by the Democrats. While a decision has been
delayed until after this week's Congressional elections, a source
close to the committee says the RNEP will get the green light.
Research into the nuclear bunker-buster follows the Bush administration's
leaked Nuclear Posture Review, which in part set out the circumstances
under which nuclear weapons might be used. It says the RNEP could
be used in pre-emptive strikes against rogue states using deeply
buried facilities to store weapons of mass destruction, for example.
The RNEP would be used on targets that may be immune to conventional
weapons. Its backers claim it would create little contamination
above ground, but critics say that it would produce huge amounts
of nuclear fallout. The RNEP may also remove the distinction between
a nuclear deterrent and conventional weapons, increasing the risk
of a nuclear exchange.

US law prevents development of new "mini-nukes" that
have an explosive yield of less than 5 kilotons. But the RNEP
falls outside this ban because it is not a new weapon. Rather,
it will be a modification of an existing nuclear bomb, probably
a highly modified B61, sources say, a weapon whose explosive yield
can be set from anything between 0.3 and 34o kilotons. The bomb
uses fission at low yields but is a fusion (hydrogen) bomb at
high yields. The Hiroshima fission bomb had a yield Of 12 kilotons.
Underground explosions are 10 tO 15 times as effective against
buried facilities as airbursts. A conventional bunker-buster is
dropped from high altitude and hits the ground at enormous speed.
It penetrates earth, rock and concrete before exploding. A nuclear
version has the advantage of a far more powerful shock wave, increasing
the depth of its destructive effect. T'he US already has around
fifty'penetrating'nuclear weapons in its stockpile, but these
can only reach a depth of six metres in earth. David Wright, a
nuclear-weapons expert at the Union of Concemed Scientists in
Washington DC, says this would not be nearly enough to contain
the radioactivity. "Even for a 0.3-kiloton explosion, you
would need a burial depth of about 70 metres in dry soil and about
40 metres in dry, hard rock to contain the blast," Wright
says. An explosion at the maximum depth achievable so far would
throw thousands of tonnes of highly radioactive debris into the
air. Moreover, Wright's calculations show that a warhead of this
size at the depths currently possible would only destroy a hardened
target buried less than 10 to 20 metres deep in rock. Some Iraqi
facilities are said to be under 6o metres of rock, requiring a
warhead of hundreds of kilotons, which would cause unacceptable
devastation above ground. But a study by the Federation of American
Scientists concludes that greater penetration with the RNEP is
unlikely, as there is a threshold at which increasing impact velocities
simply cause the warhead to deform and melt. Attempting to make
the RNEP and its warhead robust enough to withstand impact will
require extensive R&D. Weapons designers at three Department
of Energy labs - Lawrence Livermore in Califomia, and Los Alamos
and Sandia in New Mexico - will have to come up with the new ground-penetration
technology. Sandia has already patented a new penetrator (see
Graphic). While the Comprehensive Test Ban Treaty bars any test
with a live warhead, this would not prevent the RNEPs use untested.

From bugs to birds to
giant reptiles, werre finally growing a Tree of Life

ONE ar science's great outstanding projects Is about to begin
- mapping what Charles Darwin called the "great Tree of Life".
When complete, the tree will finally reveal how all IMng creature
are related to one another. The fimt projects, funded by the US
National Science Foundation, were announced last week and will
unrdvel the secrets of plants, spiders, birds and dinosaurs among
others. But the whole pmgramme Is expected to take more than a
decade. "The fundamental question of biology is the connection
among species on the Earth," says Shannon Hackett of the
Field Museum of Natural History in Chicago. Making those connections
will help researchers conserve species, restore ecosyslems and
control invading spedes. Medical researchers can use evolutionary
data to trace the origin and spread crf diseases, and to develop
new medicines. Assembling the complete tree is no mean feat. Generations
cvf biologists have sketched broad evolutionary patterns bet6veen
groups crf plants and animals and we have described around 1.7
million lmng species. But most are little studied, and millions
of other I!Wng species have yet to be catalogued. The Tree of
Life project will take advantage of the latest techniques in molecular
genetics and computer technology in a bid to reolve long-standing
debates over the interpretations of morphologic data. Genedc tests
can distinguish between species that look nearly identical, and
DNA comparisons can tell you how long since the species diverged.

"The fundamental question of biology is the connection
among species on the Earth"

The extent af genetic divergence can reveal long-lost relationships
between highly evolved species, such as the links betneen whales
and their nearest land-dwelling relations. The fimt grants will
pay fbr the mapping of seven key parts of the Tree (yf Life. At
the base of the tree, the ln@ fbr Genomic Research in Rockville,
Maryland, will fully sequence several diverse types cyf lltde-studied
bacteria in a bid to find out how they are related and trace the
development cvf photosynthesis. A team led by Chadle O'Kelly of
the Bigelow Laboratory fbr Ocean Silences in Maine will analpe
DNA ftm 50 VM of green algae and plants, and then use traditional
morphology to identify fundamental dmsions among non-flowering
plants. ether groups will collect and analyse genetic and morphological
data on over 1000 species of nematodes and 500 genera of spiders.
Hackett's group will collect DNA sequence data ftm some 500 bird
species, hoping to learn how modern birds diversified, and how
their behaviours and other traits evolved. A separate project
will build a database including digital photographs and l features
of every signlflcant specimen of the predatory dinosaurs called
theropods, thought to have given dse to birds. This will allow
researchers to compare specimens at a more detailed level than
before - previous studies only looked at the differences between
theropod genera, says dinosaur project head Mark Norell of the
American Museum of Natural History. The scientists involved will
have to come up with new ways of storing and searching data in
order to handle the vast expanse of information. But Norell hopes
to make the Tree of Life database so intumm that researchers can
compare specimens at their desks, in@ of flying to museums around
the wodd. Jeff Hecht *

Why copy protection on
CDs is worthless

THE technology built into some CDs to stop people copying them
is futile. So says a computer scientist who has put today's antipiracy
systems under the microscope. He believes the continual software
and hardware upgrades issued by the makers of computer CD drives
and audio CD players render copy protection systems pointless
in the long run. John Halderman, a computer scientist from Princeton
University in New Jersey, plans to show delegates at a digital
copyright conference in Washington DC next week that the idea
of CD copy-prevention is "fundamentally misguided".
Princeton University scientists last year debunked the technology
the music industry planned to use to inaudibly watermark sound.
Halderman is now doing a similar job on copy prevention systems.
Halderman looked at three widely available copy-protected CDs.
He found that the three different copy protection formats they
used all had one thing in common: they all index the contents
of music discs using a system meant only for recording CDs on
a computer's CD drive. A conventional music CD has an electronic
table of contents at the beginning of each disc. But a PC-recorded
CD has several tables, with a new one written every time a new
recording session adds something to the disc. Each of these tables
points back to the previous one. Personal computer CD drives read
the last, most recent table first and work back through the series
of indices - but audio CD players read only the first table. A
CD containing a copy- prevention system indexes the music correctly
in the first table but then adds dummy tables containing deliberate
errors. So CD players that read only the first table will play
the music normally. But PC CD drives - which people use for copying
- look at the last table, see garbage, get confused and play or
record nothing. Unfortunately, some audio CD players and in-car
players use PC CD drives, and will not legitimately play a protected
CD you've paid for. Nor can people play music CDs on their PCs.
But all these measures can be sidestepped, says Halderman, thanks
to the computer industry's habit of continual upgrading and bug
fixing. Makers of CD players and CD-ROM drives only need to make
"relatively simple modifications" to their software
and supposedly protected CDs can be played with ease. So playback
and recording equipment is becoming resistant to copy- prevention
techniques. "Software upgrades can be delivered easily using
the Internet," says Halderman, "and this will permanently
undermine the usefulness of audio CD copy prevention." To
ban upgrades, he argues, would lead to "buggy software and
poor hardware." The record industry could lose a fortune
if people stop buying CDs and make their own copies. Halderman
reckons he has a solution for them. "Reduce the cost of new
CDs; if discs cost only a few dollars each, buying them might
be preferable to spending the time and effort to make copies or
find them online:' Barry Fox

Cloned stem cells may
give you a new lease of life

S--Y-L--V-I--A --WESTPHAL, BOSTON

CLONEDstemcellsmaybe 11 younger", "fitter" and
much better at replacing tissue damaged by disease or age than
those from other sources. If confirmed, the finding will provide
a major boost for therapeutic cloning. The idea of therapeutic
cloning is to take adult cells from a person's body, create cloned
embryos and extract embryonic stem cells that can turn into a
wide range of tissues, all a perfect match for the patient. But
recent research suggests that stem cells in adults are just as
versatile as embryonic ones, which might make cloning unnecessary.
NowNewScientisthas uncovered a patent application that claims
cloned stem cells have a big advantage over other stem cells.
A team at Advanced Cell Technology (ACT) in Massachusetts, working
with Malcolm Moore of the Memorial Sloan-Kettering Cancer Center
in New York, cloned skin cells from two cows and injected blood-
forming stem cells (which also give rise to immune cells) from
the cloned fetuses back into the cows. One cow had its immune
systems suppressed with drugs. The cloned cells seemed to have
an amazing ability to take over from adult ones, replacing up
to 50 per cent of the cows'blood stem cells after just one infusion,
even in the cow whose immune system was untouched. The team thinks
the stem cells could be "younger" and more competitive
as a result of cloning. "We can confirm that we have had
success," says Robert Lanza of ACT, who declined to comment
on details and wanted it made clear that the company did not seek
to make the research public prior to journal publication. ACT
has been criticised for this before. The obvious implication is
that you could replace the immune system of people with leukaemia
or autoimmune diseases such as arthritis. "It would be great
if we could do this in humans," says stem cell specialist
Diane Krause of Yale University. She says it's risky to use blood
stem cells from a cancer patients' own bone marrow to restore
their immune system, as some might be cancerous. And when patients
are given bone marrow cells from donors, these can tum on their
new host. The cloned cells could also be modified before being
implanted, Lanza says. For example, cells from an HIV patient
could be altered to resist the virus. Perhaps most significantly,
people who get "younger" cells derived by therapeutic
cloning might end up with stem cells that have significantly improved
repair capabilities. Blood stem cells are known to help repair
other organs, though this ability wanes with age. "We could
introduce cells with regenerative ability," says Lanza. The
cloned cells may be more vigorous because nuclear transfer - the
key step in cloning - restores the "fuses", or telomeres,
on chromosomes, which burn down as cells divide (see New Scientist,
6 May 2000, P 4). Of course, a greater ability t6 divide and regenerate
also means a greater risk of the stem cells becoming cancerous.
And there is some evidence that cloning can disrupt normal gene
expression - some cloned animals are stillborn or have abnormalities.
Another major issue is the fact that the blood stem cells injected
into the cows came from loo-day- old fetuses, since that's when
the cells can be found in the liver and can be easily harvested.

"People who get'younger cells derived by therapeubc cloning
might end up with stem cells that have significantly improved
repair capabilites"

There's no question of allowing human cloned embryos to grow
to that stage to harvest stem cells, but Lanza says ACT and others
are trying to derive blood stem cells directly from embryonic
ones. Other experts are reserving judgement until the work is
published. "It makes me sceptical because I can't understand
from a patent application what they are doing," says another
stem cell researcher, Dan Kauftnan of the University of Minnesota.

Ecstasy has a dramatic
effect on Parkinson s symptoms

DAVID CONCAR

A FEW weeks ago ecstasy was condemned for causing Parkinson's.
Now, in a complete turnaround, it's being hailed as the key to
better treatments for the disease. Animal studies have confirmed
anecdotal reports that ecstasy can dramatically curb the uncontrollable
arm and leg movements that plague so many people with Parkinson's.
But the finding may be of little immediate help to sufferers.
The researchers aren't calling for patients to be given legal
supplies of ecstasy (MDMA). Instead, they want to look for related
drugs with the same beneficial effects. And patients are being
warned against trying MDMA for themselves. "It's impure,
illegal and dangerous," says Robert Meadowcroft, policy director
of Britain's Parkinson's Disease Society. Others are calling for
further animal studies to establish the effective dose, followed
by human trials. "People who are suffering should have the
right to decide carefully for themselves whether or not to take
MDMA," says American drugs policy campaigner Rick Doblin.
His organisation, MAPS, recently won approval from the Food and
Drug Administration for a human trial of ecstasy for treating
post- traumatic stress disorder. The latest study was prompted
by the experiences of a former stuntman, Tim Lawrence. He made
headlines when he claimed in a BBC TV documentary that "E"
enabled him to regain control of his body for hours at a time.
Parkinson's experts at the University of Manchester decided to
test Lawrence's claims. Concerns about the dangers of MDMA ruled
out human trials, says team member Jonathan Brotchie, who now
runs Manchester-based biotech company Motac. So the researchers
tumed to marmosets with a form of the disease. Parkinson's is
caused by a loss of the dopamine-producing cells in the brain.
Symptoms include rigidity and a shuffling gait. Since the late
196os doctors have treated it with L-dopa, a chemical precursor
to dopamine that can 11 unfreeze" patients. The downside
is that patients develop uncontrollable movements after taking
L-dopa for a while. Their condition tends to oscillates between
flailing limbs while on the drug and immobility off it. To mimic
Parkinson's, they gave six marmosets a chemical that kills dopamine
neurons.

"People who are suffering should have the right to decide
carefullyfor themselves whether or notto take MDMA!'

Then, over the next few months, the monkeys had daily doses
of L-dopa until they developed the usual side effect of uncontrolled
movements. At this point the animals were given MDMA. The effects
were dramatic. Normally, monkeys on L-do0a move their arms and
legs around in a repetitive and uncontrolled way virtually all
the time. But in the six hours after a dose of MDMA, these movements
happened no more than 15 per . cent of the time. MDNM somehow
reduces the debilitating side effects of L-dopa without blocking
its beneficial effects. "The magnitude and quality of the
effect took us by surprise," says Brotchie, whose team's
findings were unveiled this week at the conference of the Society
for Neuroscience in Florida. "It was always possible that
Tim's response to ecstasy was unusual.' The researchers suspect
the finding reflects MDMA's ability to stimulate the release of
the neurotransmitter serotonin in the brain. That might make up
for a lack of serotonin caused by taking L-dopa for prolonged
periods, says Brotchie. However, there are fears that MDMA can
damage serotonin-producing cells. And last month the joumal Science
published a paper claiming that MDMA can actually cause the type
of damage to dopamine cells that can lead to Parkinson's. But
the evidence was far from conclusive (New Scientist, 5 October,
p 26).

Eightfold Way Octonians and the laws of Nature

1,2,4,8 What comes next? Nothing. i If we're talking numbers,
the obvious next term is 16. But if we're talking a particular
kind of algebra, there is no next term. And it tums out that this
is highly significant. The ultimate number- the humble 8 - lies
at the heart of a mathematical system known as the octonions,
and this system appears to be the key that will allow physicists
to fit quantum theory and gravity together. Strange as it may
seem, the number 8 may provide us with a "theory of everything".
The tale of the octonions begins in the mid- 16th century. Until
that time, mathematicians had thought that numbers were God-given,
a done deal. No one could contemplate inVenting a new number.
But around 1550 the Italian algebraists Girolamo Cardano and Raphael
Bombelli did just that, by writing down the square root of -1.
It took about 400 years to sort out what the thing meant, but
onlY 300 to convince mathematicians that it was too useful to
be ignored. By the 18oos, Cardano and Bombelli's concoction had
crystallised into a new kind of number, i, whose square is -1.
The square of a "real number" - the usual kind that
we all know - is always positive. So whatever i may be, it's not
a real number, and mathematicians call it an "imaginary"
number to make this clear. A combination of real and imaginary
numbers, like 4 + 5i, is said to be "complex". We live
in a curious Universe in which, as physicist E@gene Wigner memorably
announced, mathematics is "unreasonably effective".
Complex numbers may seem weird, but they turn out to be a marvellous
tool for understanding physics. Problems of heat, light, sound,
vibration, elasticity, gravity, magnetism, electricity and fluid
flow all succumbed to this complex weaponry - but only for physics
in two dimensions. Our own Universe, however, has three dimensions
of space - if not more. So, since the two-dimensional system of
complex numbers was so effective for two-dimensional physics,
might there be an analogous three- dimensional number system that
could be used for physics in the real world? The answer is a resounding
no. The Irish mathematician William Rowan Hamilton spent years
trying to find a three-dimensional number systi!M - burwith no
success. Then, on 16 October 1843 he had a flash of insight: don't
look in three dimensions, look in four. And it worked. Hamilton
named his new numbers quaternions". Two months later, having
heard about quaternions from Hamilton, John Graves - a British
mathematician and an old college friend of Hamilton's - announced
he had found an eight-dimensional number system. He called it
the "octaves". But before Graves could publish, the
British lawyer- mathematican Arthur Cayley made the same discovery,
and published it as an addendum to an otherwise awful paper on
elliptic functions. He called the system "octonions".
The discovery of the octonions was ever after credited to the
wrong person (they are often known as Cayley numbers, even today),
but it didn't really matter because nobody took any notice of
them anyway. The octonions appeared to be nothing more than Victorian
mathematical whimsy. Graves was not to be put off though, and
spent a long while convinced that his method of going from 4 to
8 could be repeated, leading to algebras with dimensions of 16,32,
64 and so on for any power Of 2. He called his 16-dimensional
algebra the sedenions, but he couldn't find a way to make it -
or any of the others - work, and began to doubt whether it could
exist. His doubt was well-founded. We now know that those four
algebras, of dimensions 1, 2,4 and 8, are the only ones that behave
remotely like ordinary real numbers. The reason is that, with
increasing numbers of dimensions, these systems obey fewer and
fewer algebraic laws - the amount of algebraic structure keeps
decreasing. Put rather too simply, by the time we reach Graves's
sedenions, there's pretty much no algebraic structure left. Real,
complex, quaternion, octonion; 1, 2,4, and 8 dimensions: even
by mathematical standards this is an odd set of tools. These four
number systems have several features in common, the most striking
being that they are "division algebras". There are many
number systems in which notions of addition, subtraction and multiplication
hold good: when these notions are applied to the integers (...
-2,-l, 0,1,2,3,...), for example, they transform two integers
into another integer. But the same can't be said for division:
divide some integers by others, for example, and the result is
often not an integer. But in these four number systems, you can
always divide and yet remain within the same system. And that's
not the only mathematical operation that sets them apart. Numbers
in these systems are the only ones to have a "norm",
effectively the number's distance from the origin (see Graphic,
page 32). With the complex numbers, the norm of x + iyiSX2+y2.
Because of the existence of a norm, and their divisibility, these
number systems are known as "normed division algebras"
' This is all very pretty, to mathematicians at least. But surely
the only really important cases are the real and complex numbers.
Well, not quite: the quaternions have shown up in some useful
if esoteric researches - fields such as abstract algebra and topology.
But it's certainly true that the octonions remained in the shadows
for a long time. In 1925 Wigner, working with the mathematician
John von Neumann, tried to make the octonions the basis of quantum
mechanics.

"The octonions started out as mathematical curiosities,
and were almost entirely ignored for l5O years, but their time
has now come"

But he failed, and the octonions slipped back into obscurity.
Until now, that is. Rather surprisingly, the octonions have revealed
themselves as the most important system of all. That's because
they are crucial to string theory, the best candidate for a physical
theory of everything. After 150 years, physics is finally telling
us the purpose of the octonions: they are essential to space and
time. String theory is an attempt to marry the large-scale geometry
of Einstein's general relativity to the small-scale uncertainties
inherent in quantum theory. Both these theories are brilliantly
successful in their own domain. But they can't be fitted together:
put into the same framework, they effectively contradict each
other. So the search has been on for a unified theory that modifies
them well enough to fit them together consistently but doesn't
destroy their existing successes. The current front runner in
this search is known as string theory. Very roughly, the traditional
idea that a fundamental particle is a featureless point is rejected,
and particles are modelled instead as tiny loops of energy - the
aforementioned strings. The loops can vibrate in ways that give
them integer quantum numbers, such as spin, charge and charm.
But all this only works if the loop is a many- dimensional surface
that protrudes beyond the familiar four-dimensional space-time,
and one of the burning questions is just how many dimensions there
are. At the moment, finding the answer seems to depend on finding
the number of dimensions where the theories work most elegantly.
And though physicists have not pinned it down precisely, they
have noticed that something rather pleasing occurs when they work
with 3,4, 6 and lo dimensions. Interestingly, each of these numbers
iS 2 greater than that of a normed division algebra: subtraCt
2 from 3,4,6 and lo, and you get 1, 2,4 and 8. And that's no coincidence:
these algebras are a vital part of the theory. Consider, for example,
the relationship between two mathematical objects: vectors and
spinors. A vector is essentially a way to describe the size and
orientation of something. Velocity, for example, is a vector because
it describes a body's speed and the direction in which it is moving.
The spinor is a more esoteric mathematical gadget invented by
Paul Dirac to describe electron spin. It tums out that the relationship
between vectors and spinors holds precisely (and only) in space-times
Of 3,4, 6, and io dimensions. This happens because, in 3,4,6,
and lo-dimensional string theory, every spinor can be represented
using two numbers in the associated normed division algebra. This
doesn't happen for any other number of dimensions, and it has
lots of nice consequences for physics. So we have four cafididate
string theories here: real, complex, quaternionic, and octonionic.
The one that is thought to have the best chance of corresponding
to reality is the lo-dimensional one, because it neatly avoids
a mass of mathematical obstacles while allowing the physics to
work properly. And, in this system, the relationships between
the properties of matter are specified by the octonions: if this
particular theory really does correspond to reality, then our
Universe is built from pairs of octonions. if lo dimensions turns
out to be not quite enough, however, it seems that the octonions
will still be found to play a vital role in the theory of everything.
The other very fashionable candidate string theory, "M- theory",
involves 11-dimensional space-time.

Although that means the vector-spinor relationship won't hold,
something almost as good does. In M-theory, the extra dimensions
don't need to be curled up tightly, so the restriction to six
extra dimensions can be relaxed to allow a seventh, but again
it doesn't work without the octonions. In order to reduce the
perceptible part of space-time from ii dimensions to the familiar
four (three space and one time), we have to hide seven of them.
We do that by rolling them up so tightly that they can't be detected.
And how do you do that? You make use of the octonions' symmetry-
The idea of symmetry - a property that allows you to move something
in a certain way and leave it looking the same - has turned out
to be central to physics, especially the quantum world.

All our theories of fundamental particles, and their strange
properties such as spin, charge and charm, which come in whole-number
chunks, boil down to symmetries. And the use of octonionic symmetry
in M-theory even gives a purpose to a mathematical peculiarity,
discovered around the same time as the octonions, whose existence
has always mystified mathematicians (see "The eightfold way").
So the efficacy of the octonions here is doubly pleasing. While
the octonions started out as mathematical curiosities, and were
almost entirely ignored for 15o years, their time has come. They
are no longer quaint Victorians, but a hefty clue to a possible
theory of everything. Daunting though their mathematics is, physicists
are beginning to take up this new set of tools and work with it.
A paper published this year by John Baez of the University of
Califonia, Riverside, has prompted much Web-based discussion between
string theorists. it all boils down to one extraordinary realisation:
the humble 8 is no longer just a number. it's our key to the Universe.

Ian Stewart is a professor of mathematics based at the University
of Warwick Fu rther reading: "The octonions" by John
Baez, Bulletin of the America n Mathematical So(iety, vol 39,
p 145 (2002)